CHEYENNE, Wyo.  The U.S. Fish and Wildlife Service has denied a petition from the state of Wyoming that had asked to remove the gray wolf population in the northern Rocky Mountains from the federal list of threatened and endangered species.

Wyoming in 2005 had asked the federal agency to establish a distinct population for the gray wolf in the northern Rocky Mountains and proposed taking that population off of the endangered species list.

Just hours before Monday's announcement, Wyoming Gov. Dave Freudenthal and state Attorney General Pat Crank released a letter in which they warned the federal agency that the state intended to sue to compel action on that petition and another petition the state had filed.

Wyoming has proposed classifying wolves as predators in much of the state, which would allow their unregulated killing in certain areas.

In its decision announced Monday, the Fish and Wildlife Service said it couldn't propose to take the wolf off the endangered species list until Wyoming approves "a wolf management plan that regulates and limits the human take of wolves" and also commits to maintaining a set, minimum population of the animals in the state.

Idaho and Montana already have had wolf-management plans approved by the federal government; officials in both those states now manage most day-to-day management responsibilities for wolves.